Endoscopic Optical Coherence Tomography (OCT) enables the assessment of the eardrum and the middle ear in vivo. However, revealing the ossicles is often limited due to shadowing effects of preceding structures and the 3D impression is difficult to interpret. To compare the identified middle ear structures, OCT and cone-beam CT of a patient were spatially aligned and showed a good agreement in locating malleus and the promontory wall. As CT imaging uses ionizing radiation and is thus limited in application, we furthermore provide a concept how radiology can be utilized as a priori knowledge for OCT imaging. Therefore, a statistical shape model derived from μCT data of temporal bone specimens was fitted to in vivo OCT measurements, potentially providing a real-time augmentation of endoscopic OCT for middle ear diagnostics in the future.
The collagen layer of the human Tympanic Membrane (TM), which is essential for sound conduction and hearing, can be assessed in vivo by using endoscopic Polarization-Sensitive Optical Coherence Tomography (PS-OCT), as we have shown recently. Since the resolution of the utilized system was limited, an ex vivo validation of the structural information is presented here. By comparing higher resolution PS-OCT images of a temporal bone specimen and Polarized Light Microscopy (PLM) of histological slices from that TM with picrosirius red staining, the microstructure is investigated.
SignificanceEndoscopic optical coherence tomography (OCT) is of growing interest for in vivo diagnostics of the tympanic membrane (TM) and the middle ear but generally lacks a tissue-specific contrast.AimTo assess the collagen fiber layer within the in vivo TM, an endoscopic imaging method utilizing the polarization changes induced by the birefringent connective tissue was developed.ApproachAn endoscopic swept-source OCT setup was redesigned and extended by a polarization-diverse balanced detection unit. Polarization-sensitive OCT (PS-OCT) data were visualized by a differential Stokes-based processing and the derived local retardation. The left and right ears of a healthy volunteer were examined.ResultsDistinct retardation signals in the annulus region of the TM and near the umbo revealed the layered structure of the TM. Due to the TM’s conical shape and orientation in the ear canal, high incident angles onto the TM’s surface, and low thicknesses compared to the axial resolution limit of the system, other regions of the TM were more difficult to evaluate.ConclusionsThe use of endoscopic PS-OCT is feasible to differentiate birefringent and nonbirefringent tissue of the human TM in vivo. Further investigations on healthy as well as pathologically altered TMs are required to validate the diagnostic potential of this technique.
Imaging the collagen layer of the human tympanic membrane, on which the human hearing ability depends, is possible in vivo by using endoscopic polarization-sensitive optical coherence tomography (PSOCT), as we have shown recently. Since the resolution of the utilized system was limited, an ex vivo validation of the structural information is presented here. By comparing higher resolution PSOCT images of a temporal bone specimen and polarized light microscopy (PLM) of histological slices cut from the same sample and stained with picrosirius red, the microstructure is investigated. Besides matching PSOCT and PLM images, the methodical differences are discussed.
Endoscopic optical coherence tomography (OCT) enables the assessment of the eardrum and the middle ear in vivo. However, revealing the ossicles is often limited due to shadowing effects of preceding structures and the 3D impression is difficult to interpret. To compare the identified middle ear structures, OCT and cone-beam CT of a patient were spatially aligned and showed a good agreement in locating malleus and the promontory wall. As CT imaging uses ionizing radiation and is thus limited in application, we furthermore provide a concept how radiology can be utilized as a priori knowledge for OCT imaging. Therefore, a statistical shape model derived from μCT data of temporal bone specimens was fitted to in vivo OCT measurements, potentially providing a real-time augmentation of endoscopic OCT for middle ear diagnostics in the future.
Endoscopic optical coherence tomography (eOCT), a depth-resolved, non-invasive, three-dimensional imaging technique, enables morphologic and functional examinations of the human tympanic membrane (TM) in vivo. To overcome the limitation of intensity-based OCT in tissue differentiation, light polarization is used here to assess collagen fibers as birefringent tissue. A fiber-based polarization-sensitive eOCT system was realized for first in vivo examinations of the TM’s collagen fiber layer, on which the acoustic and mechanical properties depend. By evaluating the local retardation, distinguishing the TM’s different tissues was possible and a comparison to microscopic ex vivo measurements was made.
Pathological alterations of the connective tissue, e.g. in succession of chronic otitis media, impair the acousto-mechanical function of the tympanic membrane (TM). Currently, none of the diagnostic techniques used in clinical practice assesses these tissue changes. By applying polarization-sensitive optical coherence tomography (PSOCT), a depth-resolved imaging technique providing additional tissue-specific contrast, local polarization changes of the fibrous layers of a human TM ex vivo were detected due to the birefringence of collagen fibers. Reconstructing and displaying local retardation from single-input PSOCT measurements enables to distinguish different tissue types which reveals the potential of PSOCT to extend conventional ENT diagnostics.
Optical coherence tomography (OCT) is a contactless and non-invasive imaging technique. Due to the high resolution of some 10 μm and the penetration depth of 1-2 mm in scattering tissue, OCT closes the gap between microscopy and sonography. Here, we present a GRIN-based endoscopic OCT (eOCT) system for middle ear diagnostics. EOCT combines the benefit of endoscopic imaging and the advantage of morphological and functional investigation of the tympanic membrane (TM). The eOCT system has a working distance of 10 mm, which results in a field-of-view of 10 mm. This allows a full three-dimensional visualization of the TM and surrounding tissue. In addition, the oscillation of the TM can be measured spatially resolved and in the frequency range between 500 Hz and 5000 Hz with 125 Hz resolution, which is realized by phase-resolved Doppler-OCT. First clinical results are demonstrated for one selected cases, a middle ear effusion.
An endoscopic optical coherence tomography (OCT) system with a wide field-of-view of 8 mm is presented, which combines the image capability of endoscopic imaging at the middle ear with the advantages of functional OCT imaging, allowing a morphological and functional assessment of the human tympanic membrane. The endoscopic tube has a diameter of 3.5 mm and contains gradient-index optics for simultaneous forward-viewing OCT and video endoscopy. The endoscope allows the three-dimensional visualization of nearly the entire tympanic membrane. In addition, the oscillation of the tympanic membrane is measured spatially resolved and in the frequency range between 500 Hz and 5 kHz with 125 Hz resolution, which is realized by phase-resolved Doppler OCT imaging during acoustical excitation with chirp signals. The applicability of the OCT system is demonstrated in vivo. Due to the fast image acquisition, structural and functional measurements are only slightly affected by motion artifacts.
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